A remote copy scheme is used for the purpose of improving the availability and data security of a system. In the remote copy scheme, for the case where data stored in a storage apparatus installed on a local site cannot be used due to some problem, the data on the local site are copied, at an appropriate time, to another storage apparatus installed on a remote site that is a place physically away from the local site.
That is, in this remote copy scheme, a storage apparatus on a local site copies the data to a remote site being geographically isolated in order to enable the recovery of data stored in a local site which are destroyed due to, for example, a natural disaster such as an earthquake or a flood, an artificial manipulation, or the like.
Storage apparatuses respectively disposed on a local site and a remote site are coupled to each other through a network such as a dedicated line. On the storage apparatus on the local site, a logical volume from which copy is made (hereinafter, referred to as “copy source volume”) is located. On the storage apparatus on the remote site, a logical volume to which copy is made (hereinafter, referred to as “copy destination volume”) is located.
The copy source volume and the copy destination volume are managed as a pair of volumes by a management computer for managing a remote copy process. The copy source volume representing a single logical volume stored in the storage apparatus on the local site is associated with the copy destination volume representing another logical volume stored in the storage apparatus on the remote site, whereby a pair of volumes is generated. Then, all the data stored in the copy source volume are, first, copied to the copy destination volume (this copy process is hereinafter referred to as “initial copy”).
When a host computer which uses the storage apparatus on the local site updates data in a copy source volume, the storage apparatus on the local site records a logical address block (hereinafter, simply referred to as “block”) where the data thus updated is stored, and transmits this block to the storage apparatus on the remote site. The storage apparatus on the remote site writes the block data received from the local site onto a copy destination volume. Once the pair of volumes is deleted, an update block management in the copy destination volume is suspended and a transfer of update data is stopped.
Meanwhile, a server virtualization technology has been increasingly employed for the effective use of hardware resources of a server apparatus. The server virtualization is a technique in which a single server apparatus is divided into multiple virtual machines and different OSs and applications operate on the virtual machines. In the server virtualization, an OS called a manager OS (This is software which is sometimes referred to as “virtualization mechanism.” More specifically, examples include VMWare (registered trademark) and Xen (registered trademark).) manages hardware resources such as a CPU, a memory, and a disk of a server apparatus, and distributes the hardware resources to each virtual machine.
The manager OS logically divides a physical disk created on a storage apparatus which the server apparatus uses, and is capable of managing the divided disks as virtual disks. It is conventional practice to store an OS, application, and data of a computer in a physical local disk, and to store an OS, application, and data of a virtual machine in a virtual disk which is created and managed on a physical disk by a manager OS. Therefore, OSs, applications, and data (hereinafter, referred to as “operation environment”) of multiple virtual machines are stored in a single physical volume. The manager OS includes a file system for managing each virtual disk, and manages each virtual disk as a file.
A disaster recovery is a function of recovering data by using the remote copy process to make redundant copies of all of an OS, application, and data of a host computer. An OS of a host computer does not operate on server apparatuses having different physical configurations. For this reason, server apparatuses corresponding to OSs to be operated need to be also provided to a remote site in order to perform a disaster recovery. On the other hand, a virtual machine is operable even on server apparatuses having different hardware configurations, and thus its application to a system performing a disaster recovery process has been studied.
The disaster recovery process of a virtual machine is performed using the remote copy process of the storage apparatus. In the case of building a virtual machine using an NAS, a remote copy can be performed using, for example, a technology described in Patent Citation 1. A conventional remote copy is performed in units of volume, but in accordance with Japanese Patent Application Publication No. 2003-015933, a remote copy is performed in units of file, using only a file updated by the host computer.    Patent Citation 1: Japanese Patent Application Laid-open Publication No. 2003-015933